Thin film manufacturing of advanced materials is widely employed in microelectronics, photovoltaics (PV), solid-state lighting, flat panel displays, magnetic hard drives, optics, and optoelectronics. In most of these and other applications, the thin films are deposited on rigid, small-area wafers in batch processes, which typically results in a high manufacturing cost when extended to large areas. The following examples in photovoltaics and large-area electronics illustrate the costs challenges.
III-V compound semiconductors (based on GaAs, InGaP etc.) are utilized in high-efficiency photovoltaics. These films are deposited by epitaxial growth on single crystal wafers such as Ge or GaAs. By far, the highest solar cell efficiencies have been achieved with III-V compound semiconductor PVs, including one-sun efficiencies over 37%. Unfortunately, these PVs are expensive because they rely on Ge or GaAs crystalline wafers, which could amount to up to 50% of the total module cost. Due to their high cost, the use of III-V compound semiconductor materials in terrestrial applications has been limited to concentrator PVs for the utilities industry.
Flexible electronics are being used for applications such as sensors, displays, radiation detectors, wearable and medical devices. Crystalline silicon fabrication platforms are costly and typically yields form factors not adequate for large scale, inexpensive flexible electronics. Hence, flexible electronics are typically made using amorphous silicon. However, the performance of amorphous silicon is far inferior to that of crystalline silicon, which limits the performance and capability of flexible electronics. For example, the carrier mobility values of amorphous silicon and organic semiconductors used in flexible electronics are about 1-10 cm2/Vs compared to about 100 cm2/Vs of polysilicon and about 500 cm2/Vs of single-crystalline Si. As a result of the low carrier mobility, key performance metrics such as switching speed of thin film transistors (TFTs) fabricated with amorphous Si and organic semiconductors are far below that of TFTs made with crystalline silicon. The below Table 1 shows the differences in characteristics between crystalline and non-crystalline materials.
TABLE 1Comparison of two major technological platforms in semiconductor electronics and photonicsCrystalline MaterialsNon-Crystalline MaterialsSubstrateSingle CrystalNon-Single CrystalCostHighLowPerformance SuperiorInferiorCharacteristicsVersatilityBrittleFlexibleAreaSmallLarge
As shown in Table 1, crystalline materials (e.g., crystalline silicon) have superior performance (i.e., high mobility), and are therefore suitable for small-area electronics, but are expensive and brittle. Non-crystalline materials (e.g., amorphous silicon) have lower performance (i.e., low mobility), but are inexpensive and flexible, and therefore suitable for large-area electronics.
To achieve fast-switching and high current thin film transistors for high performance flexible electronic devices, there is need in the art for epitaxial films with high mobility and low carrier concentration levels. Thus, there is need in the art for semiconductor devices and corresponding methods of manufacturing same which achieve high mobility and low carrier concentration levels.
Ion Beam Assisted Deposition (IBAD) has been demonstrated as a method to grow epitaxial films on inexpensive metal substrates. Currently, IBAD templates are being used to fabricate epitaxial germanium on inexpensive metal substrates to achieve a high mobility. Silicon is, however, used primarily in most flexible electronics applications. An e-beam evaporation process has been used to fabricate epitaxial silicon on IBAD template with a hole mobility of 89 cm2/Vs at doping concentration 4.4×1016 cm−3. In the e-beam evaporation process, the silicon was grown on r-plane alumina, which suffers from a large lattice mismatch. To date, however, no one has been able to fabricate silicon films on flexible substrates with a mobility (i.e., of either or both the entire semiconductor device or the silicon film(s) themselves) higher than 100 cm2/Vs or carrier concentration levels of the silicon film(s) of less than 1016 cm−3.
Thus, there is need in the art for semiconductor devices and corresponding methods of manufacturing semiconductor devices by, inter alia, fabricating silicon on flexible substrates that will achieve high carrier mobility at low carrier concentration levels.